Hierarchical Nanosheets Research Articles

Artificial Heterointerfaces Achieve Delicate Reaction Kinetics towards Hydrogen Evolution and Hydrazine Oxidation Catalysis.

Electrochemical water splitting for H2 production is limited by the sluggish anode oxygen evolution reaction (OER), thus using hydrazine oxidation reaction (HzOR) to replace OER has received great attention. Here we report the hierarchical porous nanosheet arrays with abundant Ni3 N-Co3 N heterointerfaces on Ni foam with superior hydrogen evolution reaction (HER) and HzOR activity, realizing working potentials of -43 and -88 mV for 10 mA cm-2 , respectively, and achieving an industry-level 1000 mA cm-2 at 200 mV for HzOR. The two-electrode overall hydrazine splitting (OHzS) electrolyzer requires the cell voltages of 0.071 and 0.76 V for 10 and 400 mA cm-2 , respectively. The H2 production powered by a direct hydrazine fuel cell (DHzFC) and a commercial solar cell are investigated to inspire future practical applications. DFT calculations decipher that heterointerfaces simultaneously optimize the hydrogen adsorption free energy (ΔGH* ) and promote the hydrazine dehydrogenation kinetics. This work provides a rationale for advanced bifunctional electrocatalysts, and propels the practical energy-saving H2 generation techniques.

Molten salt template-assisted synthesis of N, S-codoped hierarchically porous carbon nanosheets for efficient energy storage

To enrich the type of carbons for double-layer supercapacitors and optimize their electrochemical performances, N/S co-doped hierarchical porous carbons (KISPCs) with well-balanced pore characteristic have been prepared by taking ginkgo leaf as carbon source and KCl/K2CO3 molten-salt as template/activation agent. The as-obtained carbons possess a well-developed interconnected sheet-like structure, accompanying with high N, S and O contents, conductive to abundant ions transport channels and exposure of more ions-accessible active sites. Moreover, the types and contents of surface functional groups of hierarchical porous carbon could also be adjusted by K2CO3 content. A symmetrical supercapacitor was assembled to validate its electrochemical performance. The KISPCs electrodes manifest a specific capacitance of 215.2 F g−1 at 0.05 A g−1, splendid capacitance retention of 78.9 % (169.8 F g−1 at 20 A g−1) and exceptional cycling stability with only 1.6 % capacity decay after 10000 charge/discharge cycles. This work can afford promising new tactics for the preparation of hierarchical porous carbon nanosheets and offer insights into the application of energy storage fields.

Hierarchical Co and Nb dual-doped MoS2 nanosheets shelled micro-TiO2 hollow spheres as effective multifunctional electrocatalysts for HER, OER, and ORR

Abstract Heteroatom doping engineering has emerged as an intriguing strategy to enhance electrocatalytic efficiency. Herein, a multiple transition metal doping approach is developed through the incorporation of both Co and Nb into hierarchical MoS2 ultrathin nanosheets directly grown on micro-TiO2 hollow spheres (Co,Nb-MoS2/TiO2 HSs) to boost the hydrogen evolution (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). The Co and Nb dual-doping effects modify the electronic structure of the host MoS2 towards maximizing the HER, OER, and ORR performance. Additionally, the unique hollow spherical structure and heterostructured synergistic effects between the TiO2 core and MoS2 shell provide effective channels for electron transfer and large surface area with abundant exposed void spaces for ion diffusion/penetration. Therefore, the Co,Nb-MoS2/TiO2 HSs catalyst demonstrates extraordinary activity and stability with small overpotentials of 58.8 and 260.0 mV at 10 mA cm−2 for the HER and OER, respectively. When employed as both cathodic and anodic electrode in an electrolyzer, the catalyst requires an operating voltage of 1.57 V to achieve 10 mA cm−2. The catalyst also exhibits great potential for the ORR with high onset potential of + 0.96 V and half-wave potential of +0.87 V, as well as direct four-electron transfer process.

Programmed exfoliation of hierarchical graphene nanosheets mediated by dynamic self-assembly of supramolecular polymers

Programming hierarchical graphene nanosheets by two-step exfoliation of graphite combined with an adenine-functionalized telechelic polymer in o-dichlorobenzene can achieve highly stable graphene nanosheets with wide-range tunable layer thickness.

Hierarchical core-shell 2D MOF nanosheet hybrid arrays for high-performance hybrid supercapacitors.

Two-dimensional (2D) metal-organic frameworks (MOFs) with large surface area, ordered pores and ultrathin thickness have recently emerged as ideal electrode materials for supercapacitors (SCs). However, their straightforward applications are restricted by the drawbacks of self-stacking and unsatisfactory electrical conductivity. Herein, ultrathin Ni-MOF nanosheets have been grafted on zeolite imidazolate framework (ZIF-L)-derived porous Co3O4 nanosheets to form hierarchical core-shell Co3O4@Ni-MOF 2D nanosheet hybrid arrays. The porous Co3O4 "core" acts as a conductive skeleton for anchoring Ni-MOF and provides shortened ion diffusion paths. The Ni-MOF "shell" can expose large active sites. Benefiting from these merits and the synergic effects of the "core and "shell", the Co3O4@Ni-MOF/NF shows a high specific capacity (capacitance) of 225.6 mA h g-1 (1980.7 F g-1) at 1 A g-1 with decent capacitance retention (82.2% after 2000 cycles). The asymmetric two-electrode cell assembled from Co3O4@Ni-MOF/NF exhibits an energy density of 37.05 W h kg-1 at a power density of 800 W kg-1 with good long-term durability (75% capacitance retention after 10 000 cycles). Moreover, two charged cells can power a red light-emitting diode (LED) for up to 16 min, manifesting the great promise of Co3O4@Ni-MOF/NF for real energy storage devices.

Carbon coated SiO nanoparticles embedded in hierarchical porous N-doped carbon nanosheets for enhanced lithium storage

Carbon coated SiO nanoparticles embedded in N-doped carbon nanosheets were synthesized via a scalable and cost-effective route, and exhibited enhanced cyclability and rate capability as an anode for lithium-ion batteries.

Electronic Modulation of Hierarchical Spongy Nanosheets toward Efficient and Stable Water Electrolysis.

The energy conversion efficiency of water electrolysis is determined by the activity of selected catalysts. Ideal catalysts should possess not only porous architecture for high-density assembly of active sites but also a subtle electronic configuration for the optimized activity at each site. In this context, the development of stable porous hosting materials that allow the incorporation of various metal elements is highly desirable for both experimental optimization and theoretical comparison/prediction. Herein, MOF-derived spongy nanosheet arrays constructed by assembly of carbon encapsulated hetero-metal doped Ni2 P nanoparticles is presented as a superior bifunctional electrocatalyst for water splitting. This hierarchical structure can be stably retained when secondary metal dopants are introduced, providing a flexible platform for electronic modulation. The catalytic origin of activity enhancement via metal (Fe, Cr, and Mn) doping is deciphered through experimental and theoretical investigations. Combining the advantages in both morphological and electronic structures, the optimized catalyst NiMn-P exhibits remarkable activity in both hydrogen and oxygen evolution in the alkaline media, with an ultrasmall cell voltage of 1.49V (at 10mA cm-2 ) and high durability for at least 240 h.

Ultrahigh surface area biomass derived 3D hierarchical porous carbon nanosheet electrodes for high energy density supercapacitors

A simple one step activation method is used to achieve an ultra-high specific surface area of 2943 m2 g−1, and abundant pore volume of 1.83 cm3 g−1 with a rational micro/meso/macro pore size distributed activated carbon nanosheets from Prosopis Juliflora wood carbon waste blocks. A superior electrochemical performance has been achieved with a specific capacitance of 588 F g-1 at 0.5 A g−1 with an excellent stability (retention 92.5% after 6000 cycles) in 6 M KOH electrolyte for a three-electrode approach. The assembled symmetric supercapacitor device outperformed in a neutral aqueous electrolyte compared to an alkaline electrolyte, such as with a gravimetric capacitance of 403 and 426 F g−1 and superior energy density of 32.9 W h kg−1 (at 172.7 W kg−1) and 56.7 W h kg−1 (at 248.8 W kg−1), and a large electrochemical window of 0–1.4 V in 6 M KOH and 0–2 V in 1 M Na2SO4 electrolyte, respectively. The electrochemical performance has been enhanced by the degree of graphitization, surface functional groups, surface area and pore structure/volume. This work provides a trustworthy approach to produce higher energy density devices from renewable biomass carbon wastes for various energy storage applications.

CoMnO2-Decorated Polyimide-Based Carbon Fiber Electrodes for Wire-Type Asymmetric Supercapacitor Applications

In this work, we report the carbon fiber-based wire-type asymmetric supercapacitors (ASCs). The highly conductive carbon fibers were prepared by the carbonized and graphitized process using the polyimide (PI) as a carbon fiber precursor. To assemble the ASC device, the CoMnO2-coated and Fe2O3-coated carbon fibers were used as the cathode and the anode materials, respectively. Herein, the nanostructured CoMnO2 were directly deposited onto carbon fibers by a chemical oxidation route without high temperature treatment in presence of ammonium persulfate (APS) as an oxidizing agent. FE-SEM analysis confirmed that the CoMnO2-coated carbon fiber electrode exhibited the porous hierarchical interconnected nanosheet structures, depending on the added amount of APS, and Fe2O3-coated carbon fiber electrode showed a uniform distribution of porous Fe2O3 nanorods over the surface of carbon fibers. The electrochemical properties of the CoMnO2-coated carbon fiber with the concentration of 6 mmol APS presented the enhanced electrochemical activity, probably due to its porous morphologies and good conductivity. Further, to reduce the interfacial contact resistance as well as improve the adhesion between transition metal nanostructures and carbon fibers, the carbon fibers were pre-coated with the Ni layer as a seed layer using an electrochemical deposition method. The fabricated ASC device delivered a specific capacitance of 221 F g−1 at 0.7 A g−1 and good rate capability of 34.8% at 4.9 A g−1. Moreover, the wire-type device displayed the superior energy density of 60.2 Wh kg−1 at a power density of 490 W kg−1 and excellent capacitance retention of 95% up to 3000 charge/discharge cycles.

Spontaneous ruthenium doping in hierarchical flower-like Ni2P/NiO heterostructure nanosheets for superb alkaline hydrogen evolution

• A Ru-doped flower-like Ni 2 P/NiO heterostructure nanosheets catalyst was prepared. • Ru-Ni 2 P/NiO/NF HNSs catalyst exhibits top-level HER activity (12 mV@10 mA cm −2 ). • XPS and DFT results reveal the electronic reconfiguration. • Superb activity originates from synergistic effect of dopants and heterostructure. Developing efficient alkaline hydrogen evolution reaction (HER) electrocatalysts remain a critical challenge for the realization of large-scale hydrogen production from water splitting, while the high energy barrier of the Volmer-step considerably impedes the catalytic activity in water-alkali electrolyzers. Herein, a novel Ru-doped hierarchical flower-like Ni 2 P/NiO heterostructure nanosheets vertically aligned on Ni foam substrates (Ru-Ni 2 P/NiO/NF HNSs) electrocatalyst is synthesized by a top-down strategy to achieve a top-level performance of HER in alkaline media. Benefitting from electronic reconfiguration, hierarchical flower-like nanosheet structure, and abundant heterogeneous interfaces, the as-obtained Ru-Ni 2 P/NiO/NF HNSs require an ultralow onset overpotential of 0 mV, a minimum overpotential of 12 mV and 112 mV to afford 10 mA cm −2 and 1000 mA cm −2 , respectively, and a Tafel slope of 22.6 mV decade −1 . Further X-ray photoelectron spectroscopy analysis combined with density functional theory calculations reveal the charge density redistribution, where electron accumulation on Ru favors the optimization of H 2 O absorption energies and the reduced energy barrier of the Volmer step, whereas the coupling effect of Ni 2 P/NiO heterogeneous interfaces is responsible for accelerating the Tafel step activity, synergistically resulting in accelerating alkaline HER kinetics. These findings reveal the significance of the rational combination of noble metal doping and heterostructure engineering toward the rational design and preparing of highly efficient electrocatalysts for the HER and beyond.

Hierarchical Pt-decorated In2O3 microspheres with highly enhanced isoprene sensing properties

For advanced fibrosis, isoprene is a typical characteristic marker that could be used to quickly screen the population for chronic liver disease (CLD). To achieve trace detection of isoprene, different mol% Pt-decorated In2O3 and pure In2O3 samples were prepared with the commonly used hydrothermal method. The obtained characterization results show that the prepared Pt-decorated In2O3 (1 mol%) sample had Pt nanoparticles uniformly attached to the surface of porous hierarchical In2O3 nanosheets, and the specific surface area was 62.3 m2/g. Subsequently, these sensors based on Pt–In2O3 and pure In2O3 nanomaterials were prepared, and their response characteristics were studied. The results show that the response of 1 mol% Pt–In2O3 to isoprene gas was significantly enhanced, and the optimal working temperature was 200 °C. The response of 1 mol% Pt–In2O3 to 5 ppb and 5 ppm isoprene was approximately 3.2 times and 25.9 times that of pure In2O3, respectively. Meanwhile, the 1 mol% Pt-modified sample exhibited excellent selectivity for isoprene relative to other biomarkers (carbon monoxide, hydrogen, ethanol, and ammonia). The sensor shows good repeatability and long-term stability. Therefore, the developed 1 mol% Pt-decorated In2O3 was expected to be applied as a gas-sensitive material for breath isoprene, which could be suitable for large-scale CLD rapid breath detection.

Selenium doped nickel nanosheet array for oxygen evolution reaction

Developing an oxygen evolution reaction electrocatalyst with low cost, abundant reserves and excellent performance is essential for the large scale application of renewable hydrogen energy. Herein, a selenium doped hierarchical Ni-based electrocatalyst was fabricated. Nickel nanosheet array (NNA) was firstly electrodeposited on stainless steel, and then selenium was doped in the NNA to form a hierarchical nanosheet structure via a hydrothermal process. The effect of hydrothermal temperature and duration on the OER performance were investigated. Results shown that after selenization at 140 °C for 12 h, the NNA electrodeposited for 30 min performed best OER performance with a current density of 50 mA cm−2 at overpotential of 365 mV and a small Tafel slope of about 34 mV dec−1. This work provides a valuable strategy to design high efficiency electrocatalysts and shows the universality of selenization for improving catalytic performance.

Template-Free Preparation of Hierarchical Porous Carbon Nanosheets for Lithium-Sulfur Battery.

Porous carbon nanosheets have the advantages of longitudinal continuity, transverse ultrathin, high specific surface area, and surface atomic activity, as well as the synergistic effect of micro and nanoproperties, so the research on their preparation, structure, and properties has attracted wide attention. A series of ultrathin hierarchical porous carbon nanosheets (HPCNs) is fabricated through carbonization of precursors obtained through the Friedel-Crafts reaction-assisted loading of polystyrene on graphene oxide. Hierarchical pore structures consist of three parts: (1) the micropores (1.3 nm), which were provided by porous polystyrene through the Friedel-Crafts reaction; (2) the mesopores (3.8 nm), which were provided by slab pores from the stack of carbon nanosheets; and (3) the pores (>5 nm) formed from the random stack of carbon nanosheets. Controlling the carbonization time and temperature adds to a prominent increase in specific surface area from 405.8 to 1420 m2 g-1. It was found that excessive carbonization would destroy the hierarchical pore structure. These porous carbon materials were used as cathode materials for lithium-sulfur battery and showed good performance. HPCN/sulfur cathode has good rate performance and cycle performance, and the capacity retention rate is 87% after the current density rises from 1 to 3 C and 91% after 200 cycles.

Hierarchical nanosheets of ternary CoNiFe layered double hydroxide for supercapacitors and oxygen evolution reaction

The preparation of stable and efficient thin films with excellent energy storage and conversion capabilities has attracted great attention in the field of supercapacitors and electrocatalysis. Herein, hierarchical nanosheets-based ternary CoNiFe layered double hydroxide (LDH) thin films are prepared via an inexpensive and facile electrodeposition method. The structural, morphological, and electrochemical properties of films are systematically studied and compared with their binary counterparts. As prepared CoNiFe LDH shows a maximum specific capacity of 360 C g−1 at the current density of 0.4 A g−1 with a capacity retention of 51% even at the higher current density of 10 A g−1. Moreover, it shows excellent cyclic stability of 84% after 2000 cycles. As an electrocatalyst, CoNiFe LDH demonstrates an excellent performance in OER, affording an overpotential of 196 mV at the current density of 10 mA cm−2 with a Tafel slope value of 49 mV dec−1. Also, it depicts excellent catalytic stability with stable operation for over 10 h. Thus, ternary CoNiFe LDH thin film can be used as a promising electrode material for both electrochemical energy storage and catalysis.

Hierarchical CoS2/N-Doped Carbon@MoS2 Nanosheets with Enhanced Sodium Storage Performance.

We introduce a hierarchical nanostructure of CoS2/N-doped carbon@MoS2 comprising two transition-metal sulfides CoS2 and MoS2, with enhanced sodium storage performance in sodium-ion batteries. A micron-sized Co metal-organic framework (MOF) is transformed into a CoS2/N-doped carbon composite, followed by a solvothermal growth of MoS2 nanosheets on the surface. The resulting composite material offers several specific advantages for sodium storage: (i) accelerated sodium-ion diffusion kinetics due to its heterogeneous interface; (ii) shortened ion diffusion path and exposed active sites for sodium storage due to its hierarchical nanosheet architecture; and (iii) homogeneous nitrogen doping of the MOF-derived carbon, which is beneficial for electronic conductivity. Due to these merits, this composite exhibits excellent electrochemical performance with a specific capacity of 596 mAh g-1 after 100 cycles at 0.1 A g-1 and 395 mAh g-1 at 5.0 A g-1.

High-Performance Supercapacitor Electrode Obtained by Directly Bonding 2D Materials: Hierarchal MoS2 on Reduced Graphene Oxide

Energy storage devices are the ultimate flexible solution to overcome energy deficiency. Need is to find innovative nanomaterials to overcome the lags in efficiency and sustainability. Herein, we report the synthesis of hierarchical MoS2/rGO nanohybrids as electrode material for supercapacitors. Pure phase and flower-shaped molybdenum disulfide (MoS2) nanosheets have been synthesized using a meek hydrothermal method followed by the preparation of MoS2/rGO nanohybrids. The physicochemical aspects have been carefully analyzed along with electrochemical properties using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) method in the 1 M KCL electrolyte. The capacitance of MoS2 and MoS2/rGO found to be 297 F/g (66 mAh/g or 238 C/g) and 850 F/g (153.5 mAh/g or 552.5 C/g) at 1 A/g respectively, with 95.3% retention in capacitance after 10,000 cycles at 2 A/g. The improved electrochemical performance of the MoS2/rGO electrode could be ascribed to rapid diffusion pathways delivered by rGO and improved redox reactions of hierarchical MoS2 nanosheets owing to the high surface area (391 m2/g). This feature enables a decrease in the entire impedance of electrodes, which agrees with the findings obtained from electrochemical impedance spectroscopy.

Vapor-Phase Furfural Decarbonylation over a High-Performance Catalyst of 1%Pt/SBA-15

A high-performance Pt catalyst supported on SBA-15 was developed for furfural decarbonylation. Compared to Pt catalysts loaded on microporous DeAl-Hbeta zeolite and hierarchical micro-mesoporous MFI nanosheet (NS) materials, the 1%Pt/SBA-15 catalyst afforded notably higher activity, furan selectivity and stability owing to the negligible acid sites and proper mesopores on the SBA-15 support. Among a set of 1%Pt/SBA-15 catalysts bearing Pt nanoparticles (NPs) with sizes of 2.4–4.3 nm, the catalyst with 3.7 nm Pt NPs afforded the highest furan selectivity. Over the optimal catalyst, 88.6% furan selectivity and ca. 90% furfural conversion were obtained at 573 K and a high weight hourly space velocity (WHSV) of 16.5 h−1. Moreover, the reaction temperatures at 440–573 K and the ratios of H2 to furfural at 0.79–9.44 did not affect the reaction selectivity notably, showing that the reaction over 1%Pt/SBA-15 can be conducted over a wide range of conditions. The catalyst was stable under the harsh reaction conditions and lasted for 90 h without significant deactivation, demonstrating the superior property of SBA-15 as a catalyst support for furfural decarbonylation.

Construction of hierarchical honeycomb-like MnCo2S4 nanosheets as integrated cathodes for hybrid supercapacitors

Bimetallic transition metal sulfides (TMSs) are one class of promising electrode materials that have attracted wide attention for energy storage applications. Herein, we have presented a moderate and efficient synthetic methodology to rationally design and construct hierarchical honeycomb-like manganese cobalt sulfide nanosheets (MnCo2S4 NSs) as integrated cathodes for hybrid supercapacitors (HSCs). The anion-exchange process performed in the sulfidation reaction has significantly improved the electrochemical performance of the MnCo2S4 NSs, resulting in a superior areal capacity of 0.837 mA h cm−2 at 3 mA cm−2, a superb rate capability, and an admirable cycling lifespan with 92.3% of the initial capacity retained after 10,000 cycles. Moreover, MnCo2S4 NSs are directly used as integrated cathode and iron oxide particles encapsulated in reduced graphene oxide (Fe2O3@rGO) is employed as the anode to assemble the HSC. The as-assembled MnCo2S4 NSs//Fe2O3@rGO HSC delivers a superb energy density of 61.4 Wh kg−1 with an admirable cycling lifespan of 90.4% of capacity retention after 10,000 cycles. Besides, two HSC modules connected in series can power a homemade light-emitting diode (LED) device for 23 min, highlighting its potential practical prospects in energy storage systems.

Surfactant-promoted synthesis of hierarchical zeolite ferrierite nano-sheets

• Hierarchical FER nano-sheets were prepared using piperidine and CTABr . • FER nano-sheets were ~10 nm in thickness, exhibiting abundant interparticle porosity . • Addition of CTABr promoted the zeolite FER crystallization . • Hierarchical FER nano-sheets exhibited improved accessibility of the active sites . • This method is facile, cost-effective and easy for scale-up.

Extended Gaussian Filtering for Noise Reduction in Spectral Analysis

We present a method of reducing noise in spectra that is based on eliminating low-order derivatives of reciprocal-space (RS) filter functions, yet ensuring that the functions roll off smoothly to minimize Gibbs oscillations. The approach takes advantage of the fact that information and noise are separated in RS. The method preserves as much information as possible, while reducing or even eliminating unwanted contributions (noise). To demonstrate the method we apply it to a model spectrum, data including an XPS spectrum of S2p in hierarchical NiCo2S4 nanosheets, and the Raman spectrum of 10-layer film of FePS3 with polarization direction of 90° with respect to the a-axis.